The use of recycled oils and renewable raw materials in the production of transportation fuels and lubricants is an object of interest. The use of renewable raw materials of biological origin instead of non-renewable fossil raw materials for production of hydrocarbon components is desirable. The fossil raw materials are exhaustible and they have harmful effects on atmosphere and environment.
Bio-oils have previously been transesterified to form biodiesel (fatty acid methyl esters; FAME) and biolubricant components (lube esters). The use of lube esters is limited to a few special applications such as oils for refrigerator compressor lubricants, bio-hydraulic oils and metal working oils. In regular automotive and industrial lubricants, esters are used mainly in additive scale, because of technical problems associated with the lube esters. Lube esters are polar compounds and suffer greater seal-swelling tendency than pure hydrocarbons. In addition, lube ester oils are hydrolyzed more easily to acids, which in turn cause corrosion on lubricating systems. Lubrication oils consisting of pure hydrocarbon structures do not suffer from these problems. It is therefore desirable to find ways of producing hydrocarbon lube oil components from renewable sources.
High molecular weight components can be produced from free fatty acids in a method where two free fatty acids react with each other forming a ketone. The carbon number of the formed ketone back-bone is the sum of the carbon atoms in the two fatty acids minus one carbon, due to the release of one molecule of CO2 during ketonization. The catalysts used in these reactions are metals or oxides of alkaline earth metals. Metal oxide catalysts do no deoxygenate the formed ketones.
Metal oxide ketonization catalysts suffer from several drawbacks. The catalysts cannot tolerate double bonds or triglycerides during the ketonization, of which both are typically present in bio-oils. Therefore, double bonds must first be saturated and triglycerides are removed prior to the ketonization unit. This is typically performed by distilling the free fatty acids and employing a pre-hydrogenation unit before the actual ketonization unit. The ketonization units therefore can require a very cumbersome pre-treatment of the triglyceridic bio-oils.
In addition, ketonization reaction of fatty acids is typically done using gas phase introduction of free fatty acids. Due to the low vapor pressure of fatty acids, vaporisation of fatty acids needs much energy and carrier gas, which can require a large unit.
Formation of hydrocarbon lube components by ketonization of free fatty acids, using a metal oxide catalyst in gas phase, is demonstrated in WO2007068795. The formed ketones were further hydrodeoxygenated and isomerized and paraffinic lube oil components were produced. EP 591297 describes a method for producing a ketone from fatty acids by pyrolysis reaction using a magnesium oxide catalyst. EP 0457665 discloses a method for producing ketones from triglycerides, fatty acids, fatty acid esters, fatty acid salts, and fatty acid anhydrides using a bauxite catalyst containing iron oxide. All these methods suffer from the above described disadvantages.
High molecular weight compounds have also been reported in publication EP1741768 as unwanted side-reaction products in hydrodeoxygenation reactions of biological oils and fats. The side-reactions, such as oligomerization and even polymerizations, are due to uncontrolled reactions involving the double bonds of the biological oils (unsaturated fatty acids). These high molecular weight compounds are a nuisance in HVO (hydrogenated vegetable oil) production in form of lowered middle distillate yield as well as coking and de-activation of the catalyst.
Publication US 2011107656 describes a method for processing triglyceride-containing, biologically-derived oils to provide for base oils and diesel fuels, wherein partial oligomerization of unsaturated fatty acids contained therein yields a mixture from which the base oils and diesel fuels is extracted. Dimerization, trimerization or oligomerization of unsaturated fatty acids forms, after hydrodeoxygenation, highly branched and cyclic hydrocarbon components and even aromatic compounds are formed. Viscosity index of these mixtures is greater than 120.
Therefore, there is an obvious need for a method to produce nonpolar saturated base oil components complying with the high quality requirements from renewable sources avoiding the above disclosed problems.